(a) Field of the Invention
The present invention relates to a hydraulic control system of a six-speed automatic transmission for a vehicle. More particularly, the present invention relates to such a control system that minimizes shift shock and reduces fuel consumption.
(b) Description of the Related Art
Typical automatic transmissions include a torque converter and a powertrain of a multiple speed gear mechanism connected to the torque converter. In addition, a hydraulic control system is provided in an automatic transmission for selectively operating at least one operational element included in the powertrain according to a running state of a vehicle.
Such an automatic transmission includes a powertrain and a hydraulic control system. The powertrain includes a compound planetary gear set, formed by combining at least two simple planetary gear sets to achieve the required multiple speeds, and a plurality of friction members. The hydraulic control system selectively operates the friction members of the powertrain according to driving conditions.
A variety of such powertrains and hydraulic control systems have been developed by vehicle manufacturers according to their own schemes. Currently, four-speed automatic transmissions are most often found on the market. However, a five-speed automatic transmission has also been realized for enhancement of performance of power transmission and for enhanced fuel mileage of a vehicle.
Recently, developing further from such five-speed automatic transmissions, six-speed automatic transmissions are under investigation such that performance of power transmission of an automatic transmission, and thereby fuel-mileage of a vehicle, are being further enhanced. Recently developed six-speed automatic transmissions achieve six forward speeds by a combination of two planetary gear sets, three clutches, two brakes, and one one-way clutch, which is simpler than a conventional five-speed automatic transmission formed by adding an additional planetary gear set to a four-speed automatic transmission.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore, it may contain information that does not form the prior art that is already known in this country to a person or ordinary skill in the art.